A typical urban residential, commercial or industrial property is serviced by many utilities, including water supply and waste drainage. The pipes which carry water into a premises on the property and drain wastewater from the premises into a sewer system are conventionally buried underground.
Utilities can be installed at different times. Particularly in the case of residential premises, the installation of a natural gas services and mains may occur many years after the premises are erected, for example when the owner changes to a gas heating system from another system or when a gas main on a street is replaced.
Gas pipes at such new installations were for many decades laid in trenches, which allowed service personnel to see the locations of existing underground infrastructure. However, trenching is an expensive and often disruptive process.
More recently, gas lines have been installed underground by guided boring devices which burrow through a landmass horizontally and create a path for a conduit such as a gas pipe. This technique is considerably less expensive and less disruptive than trenching. However, it has the disadvantage that service personnel cannot see what is beneath the land mass in order to avoid obstacles such as pipelines for other services.
The safe installation of utility lines in built up or established areas by horizontal drilling or “torpedoing” requires knowledge of the exact location of other utility lines, so that they may be avoided during installation. Waste drainage and sewer pipes are particularly problematic because of their relatively large size and composition.
Sewer laterals and other waste drainage pipes may be composed of metal or clay or, in the case of newer houses, plastic such as polyvinyl chloride (PVC). Such pipes are typically four to six inches in diameter and buried four to seven feet beneath the surface of the ground. However, the locations of waste drainage pipes are not consistent, particularly in neighbourhoods where the housing may be very old.
If a horizontal drilling device encounters a clay or plastic drainage or sewer pipe in the course of operation, it will typically punch through the pipe (often unbeknownst to the operator). The gas pipe can then be installed through the sewer lateral or other waste drainage pipe. This can lead to many potential problems, including leakage of wastewater into the ground surrounding the property or potentially a build-up of gas within the drainage or sewer pipe.
A number of technologies and techniques are used today to locate electrical, telephone and water utilities. For example, in many common ground conditions metal detectors can be used to locate metal pipes. However, other than trenching, there is no method for consistently and precisely locating buried non-metallic pipes, such as plastic or clay drainage or sewer pipes. Neither clay nor plastic is electrically conductive, so most techniques used for locating other types of utility lines are ineffective. For example, metal detectors cannot detect clay or plastic. Also, in regions where the soil consists of a great amount of clay from three feet down, the use of ground penetrating radar, which is a popular method of utility line location, is ineffective.
Newer non-metallic waste drainage and sewer pipes may be equipped with a conductive wire extending along their length. An electrical signal transmitted through the wire can be detected by surface equipment, thus providing the location and direction of the pipe (and in some cases an estimate of its depth). An example of such surface detection equipment is the RD4000 Transmitter/Receiver by Radiodetection (Trademark). However, this methodology requires that the pipe to be located be equipped with a conductor (essentially an antenna) through which the locating signal can be transmitted for sensing by the receiver.
There is thus a need for a system and method which can accurately and consistently locate buried non-metallic pipes such as plastic or clay waste drainage or sewer pipes that are not equipped with an electrical conductor, from above-ground.